1. Field of the Invention
This invention relates to body worn transmitters and methods for determining if tampering has occurred. More particularly, it refers to methods of detecting removal of a transmitter without inhibiting the subject's ability to perform his or her occupation.
2. Description of Prior Art
Body worn transmitters containing tamper detection elements are used today with a fixed position monitoring receiver for the purpose of house arrest, curfew sentencing, pre-trial sentencing, parole and probation. Today, tamper detection only can be reported while the body worn transmitter is communicating with an associated monitoring receiver in a fixed location. Recently, portable monitoring receivers for body worn transmitters determining location using radio triangulation have been designed to report the location of tampering with a body worn transmitter whenever and wherever such tampering occurs. The current house arrest tamper detection systems however, do not allow subjects to have occupations requiring them to be immersed in water above the body worn transmitter. Such immersion in water prevents operation of the transmitter to the associated monitoring receiver. Either being immersed in an electrolyte solution or not being able to communicate with the monitoring receiver due to immersion results in potentially false tampering reports.
Currently, determining tampering with a body worn transmitter is accomplished by using either embedded wires or fiber optics in a strap attached to the transmitter. The transmitter is attached with the strap either at the ankle or wrist of the subject. A continuity circuit through the strap using either wires or fiber optics detects if the attaching strap has been severed. There is a problem with each of the wires or fiber optics. In the case of continuity wires embedded in the strap, jumper wires can be used to circumvent the continuity circuit. In the case of fiber optics, clean and optically flat connection interfaces are difficult to achieve when cutting the strap for fitting around the ankle or wrist of the subject, thus requiring optical interface gels or oils which could leach out of the connectors from repeated immersion causing false tampering signals. These devices can be seen in U.S. Pat. Nos. 5,298,884, 5,523,740, 5,504,474, 4,980,671, 5,014,040, and 4,812,823.
Other systems to detect the close proximity of the subject to the transmitter employ a passive proximity circuit or electric potential detector requiring additional wires embedded in the strap to function as an anode and cathode. This system determines capacitance change with distance changes between the strap and the human body. Since the detector is passive and uses an amplifier for gain to measure capacitance of the human body, slight movements of the body worn device erroneously can register as tampering signals. Since the body is mostly comprised of salt water, immersion of proximity sensors in a saline solution masks the effects of removing the transmitter since the electrolytic nature of the saline solution exhibits the same capacitance as the human body. While immersed, the transmitter cannot radiate to the associated monitoring receiver because the transmitted signal is attenuated with the antenna immersed. For this reason, immersion in an electrolytic solution, such as a chlorine solution or brackish water will register as a tampering signal for the transmitter as described in U.S. Pat. No. 5,298,884.
A transmitted signal from the current body worn transmitters is capable of being recorded using a scanner and retransmitted using a signal generator in order to mislead the monitoring receiver. Such action would allow transmitter tampering to occur without detection by the monitoring receiver. Body worn transmitters need to latch when tampering is detected. If a notification of tampering is determined to be false, then a system to reset the tamper latch remotely is desired to remove the need to physically reset the tamper latch on the body transmitter.
There exists a need to improve detection of tampering with body worn transmitters. In addition, subjects wearing transmitters having occupations requiring physical activity generating sweat or immersed in electrolyte solutions above the body worn transmitter need to be protected from the generation of false tampering signals. In the case of a confirmed false tampering signal, there is a need for a system to reset the tamper latch as set forth above.
The integrity of the signal between the body worn transmitter and the monitoring receiver also needs to be improved to prevent misleading tamper detection signals generated by the body worn transmitter or masking of the tamper detection signal by the subject.